Ionic conductivity in polyphosphazene polymer electrolytes prepared by the living cationic polymerization

Two polyphosphazene-based electrolytes were synthesized. The first was the polymer electrolyte poly[bis(methoxy-ethoxy-ethoxy-)phosphazene] (MEEP) with lithium triflate, the second was sodium salt of sulfonated poly[bis(phenoxyethoxy)phosphazene] (PhEP) as a polyelectrolyte. The “living” cationic polymerization of the monomer Cl 3PNSi(CH 3) 3 was used to obtain the polymer precursor poly(dichlorophosphazene). The final polymers were obtained from the precursor by nucleophilic substitution. The monomer was synthesized via a recently reported route. The emphasis lied on testing the accessability and properties of electrolyte materials obtained by the newer synthetic techniques. The chosen synthetic approach proved to be a suitable and straightforward access to functionalized polyphosphazenes and therefore to corresponding polymer-based electrolytes. The ionic conductivity was studied by impedance spectroscopy in the temperature range between 20 and 70 °C. The temperature dependence of the conductivity of MEEP/LiCF 3SO 3 is described by the Vogel–Tamman–Fulcher (VTF) equation. At 25 °C, its conductivity was 10 −5 S cm −1. The conductivity of the sodium salt of sulfonated PhEP was especially sensitive to a changing water partial pressure and is useful as humidity-sensitive sensor. In the presence of a water-saturated atmosphere, sulfonated PhEP showed a conductivity of 4.7×10 −2 at 25 °C.